Eductor cooled gas turbine casing

ABSTRACT

A cooling arrangement for a gas turbine power plant is disclosed in which cycle air is used in combination with atmospheric air as the cooling fluid. A plurality of eductor tubes with nozzles are disposed about the turbine casing and serve to direct pressurized cycle air into associated cooling holes. The cycle air gives momentum to the secondary atmospheric air and the cooling medium passes through the holes, removing heat therefrom. The use of cycle air in combination with atmospheric air also provides for compartment ventilation in a gas turbine of the enclosed type.

United States Patent 2,591,399 4/1952 Buckland Inventors Richard W.Gentile Schenectady, N.Y.; Wayne B. Moyer, deceased, late ofSchenectady, N.Y. by Carolyn Moyer, executrix Appl. No. 849,272

Filed Aug. 4, 1969 Patented Jan. 4, 1972 Assignee General ElectricCompany EDUCTOR COOLED GAS TURBINE CASING 10 Claims, 3 Drawing Figs.

US. Cl 60/39.66,

415/116, 415/175 Int. Cl F02c 7/18 Field of Search 60/3966;

References Cited UNITED STATES PATENTS 2,840,986 7/1958 Davies 60/39663,043,561 7/1962 Scheper.. 415/115 2,372,467 3/1945 Alford 415/1752,625,009 1/1953 Leggett 60/3966 2,652,216 9/1953 Hoffman 60/39662,940,258 6/1960 Lombard 415/175 Primary Examiner-Douglas HartAttorneys-William C. Crutcher, Frank L. Neuhauser, Oscar B. Waddell andJoseph B. Forman ABSTRACT: A cooling arrangement for a gas turbine powerplant is disclosed in which cycle air is used in combination withatmospheric air as the cooling fluid. A plurality of eductor tubes withnozzles are disposed about the turbine casing and serve to directpressurized cycle air into associated cooling holes. The cycle air givesmomentum to the secondary atmospheric air and the cooling medium passesthrough the holes, removing heat therefrom. The use of cycle air incombination with atmospheric air also provides for compartmentventilation in a gas turbine of the enclosed type.

PATENTEUJAN 4:972 363L672 INVENT RICHARD W. GE LE, WAYNE B. MOYERDECEASED, BY CAROLYN S. MOYER,

EXECUTRIX.

THEIR ATTORNEY.

EDUCTOR COOLED GAS TURBINE CASING BACKGROUND OF THE INVENTION Ingeneral, this invention relates to an improved cooling arrangement forhigh temperature elastic fluid machines. More particularly, it relatesto a cooling arrangement whereby the turbine casing and exhaust frame ofa gas turbine power plant are cooled by using pressurized cycle air incombination with atmospheric or secondary air.

It is well known that the efficiency and output of an elastic fluidmachine, in particular a gas turbine power plant, can be increased byincreasing the operating temperature of the elastic fluid. Of course, asthe temperature of the elastic fluid increases, the structural elementsof the machine must be redesigned and/or cooled in order to maintainclose tolerances, and the like.

One of the structural elements which usually requires a cooling means ifit is to operate efficiently at high temperature, is the turbine casingor shell. Ideally, a turbine shell cooling arrangement would be one thatallows ease of construction, efficient and effective heat exchangecharacteristics, economy of manufacture, and simplicity and reliabilityduring operation. Another such element which may require a cooling meansis the exhaust frame. Of course, it will be understood that otherelements may be cooled and the two mentioned are by way of illustrationonly.

Prior to the present invention, one method of cooling a turbine shellwas with the use of a closed circuit water cooled system. This systemwas very detailed in design and required many collateral elements otherthan just the cooling jacket around the shell. Difiiculties areencountered at casing connecting joints. A further problem associatedwith a water cooled system was that high thermal stresses were inducedin the shell, thus precluding the choice of lower cost casing materialswhile adding to the clearance problem. It would be desirable to simplifythe design of the cooling system and at the same time provide uniformcooling.

It is well known that other elements within a gas turbine power plantmay be cooled by the circulation of cycle air. A slight loss inefficiency does result from the use of cycle air, but the advantagesmore than compensate for the loss in efficiency. Being a simple andeconomic method for cooling gas turbine elements, it would be desirableto cool the turbine casing in a like manner, which utilizes cycle airand atmospheric air to provide the necessary pressure rise and flow toaccomplish complete cooling of the hot casing areas of the gas turbine.

Power plants of this variety which are installed outdoors usually arecompletely enclosed in order to provide protection from harsh weatherconditions. Between the casing areas of the power plant and the outercover, there are formed various compartments or air spaces. Air isallowed to enter the compartments in order to act as a heat exchangefluid, removing some of the heat generated by the hot casings, but, as aresult of the heat exchange, it is necessary to provide a ventilationmeans so as to establish effective heat exchange between the hot casingareas and circulating atmospheric air.

Accordingly, the primary object of the present invention is to utilizecycle air in combination with atmospheric air as the cooling fluid forthe hot turbine casing.

Another object is to provide a cooling system which is simple inoperation and design.

Still another object is to provide uniform cooling about the hot casingareas.

Still a further object of the invention is to provide means for improvedcompartment ventilation.

SUMMARY OF THE INVENTION Briefly stated, the invention is practiced byproviding cooling holes in a gas turbine casing and a plurality ofeductor tube with nozzles about the circumference of the casingpositioned so as to discharge a pressurized fluid into the coolingholes. The pressurized fluid mixes with the secondary atmospheric airsurrounding the casing, thus causing the cooling mixture to flow throughthe holes which results in heat exchange between the casing and thecooling fluid flow.

DRAWING These and many other objects of the invention will becomeapparent by reference to the following description, taken in connectionwith the accompanying drawing, in which:

FIG. 1 is a cutaway view, partly in section, of that part of a gasturbine plant which embodies the present invention.

FIG. 2 shows part of the turbine casing with the details of the presentinvention.

FIG. 3 shows part of the turbine casing with an alternate embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT R Referring now to FIG. 1 of thedrawing, that part of an axial flow gas turbine is shown which ismaterial to the present invention. It should be recognized that althoughthe elements shown are those of a gas turbine power plant, other typesof elastic fluid machines could be adapted to include the concept of thepresent invention.

The construction and operation of an axial flow gas turbine are wellknown in the art. Hence, only a general description of those elementsnot material to the present invention will be made.

FIG. I shows three sections of the gas turbine beginning with thecombustion chamber wrapper indicated as I, the turbine shell or casing2, its axial length indicated by the bracket, and the exhaust framesection generally indicated as 3. Not shown is the compressor section.Surrounding the gas turbine casing in general is outer cover 20 whichprotects the gas turbine components from inclement conditions. It fonns,in combination with the power plant an outer compartment or airspace 3awhich is open to the atmosphere at various points. Of course, it will beappreciated that an outer cover is not an essential working element of agas turbine but that it is only employed when conditions warrant. Beforepassing to a description of the internal elements in the gas turbine, itshould be noted that it is from this outer compartment whichcommunicates with the atmosphere that the secondary air is derived forthe operation of the eductor cooling system. Of course, if the outercover is not utilized, the secondary air will be derived directly fromthe atmosphere. This will be better understood when referring to theoperation of the invention. The structure surrounding turbine willhereinafter be referred to as the gas turbine casing.

The cutaway portion of FIG. 1 shows the elements within the turbinesection 2 and exhaust frame section 3 including two nozzles 4 and 5which direct the motive fluid flow into the buckets 6 and 7 of atwo-stage turbine. Buckets 6 and 7 are of the type which are mountedcircumferentially on a rotor wheel so as to rotate about the axis of thegas turbine when a motive fluid impinges upon their surface.Circumferential flow guides 8, 8a serve two main function; first, todirect the motive fluid as it leaves the first turbine stage andproceeds past the diaphragm assembly 40 to the second nozzle 5, andsecond, to form an annular internal compartment 9. The inner compartment9 is formed in conjunction with the upper flow guide 8, two shroudmembers 10, I1, and the turbine casing 2. Compartment 9 has means toadmit a pressurized fluid generally consisting of clean cycle air whichserves as the primary fluid for the eductor cooling system. Although theorigin is not material to the present invention it should be noted thatthe pressurized fluid may be derived from several different sources. Onesuch source is compressor extraction air which is bled from a stage ofthe compressor and direction to compartment 9. In FIG. I, a possibleflow path for pressurized air from the combustion chamber wrapper I, andhence from the turbine compressor stage to the compartment 9, isindicated by a plurality of arrows. Pressure differentials, as well assegmented seals of the type shown in US. Pat. Nos. 3,043,561

and 3,412,977 granted to Scheper, Jr. and Moyer et al., respectively,motivate and allow pressurized air to flow from the compressor stage tothe compartment 9. it will be appreciated that cycle air may serve asthe pressurized fluid although it is not limited to this source, and, infact, an external source of pressurized fluid could be provided. Cycleair from the compressor stage or from an external source may be drawnthrough an external pipe which is attached at one end to the source ofthe pressurized fluid and attached at the other end to ring manifold 32which girds the turbine shell 2. This ring manifold will then externallyperform the same function as internal compartment 9 inside the turbineshell.

The exhaust frame section 3 is structurally composed of struts 12 whichare attached to an outer barrel l4 and an inner barrel 14c. Forming theexhaust diffuser are circumferential exhaust sidewalls 13, 13a,constructed similarly to flow guides 8, 8a, and which are located in theexhaust frame section 3 between the inner and outer barrels in order todirect the exhaust gases from the last stage of turbine buckets 7 to theatmosphere or to a heat recovery unit should one be employed. Similar tocompartment 9 is circumferential annular exhaust compartment which isformed by the upper exhaust sidewall 13 and the outer barrel 14. One endof strut 12 is open to exhaust compartment 15 for the passagetherethrough the cooling medium as will be more fully understood underthe operation of the invention. The opposite ends of struts 12 are openand communicate with the atmosphere; that is, after the cooling mediumpasses through struts 12, it is then eventually directed to theatmosphere as seen by the arrows in FIG. 1.

The exhaust frame section 3 is connected to the turbine casing 2 at anaxial position indicated as 16. In a like manner, the combustion chamberwrapper 1 is connected to the turbine casing 2 at an axial position 17.

Referring now to both FIGS. 1 and 3, wherein like numbers represent likeelements, an eductor tube 18 is shown as disposed in the turbine casing2. it is noted that a plurality of eductors are positioned about thecircumference of the turbine casing in order to provide adequate anduniform cooling. The eductor tube 18 is constructed of small diametertubing with a 90 bend. On one end of tube 18 is a simple convergingnozzle 19 which is generally directed in an axial direction; that is, itis directed in the same general direction as is the turbine casing 2 andouter barrel 14. The end of eductor tube 18 opposite the nozzle 19 opensinto compartment 9 where it receives the pressurized fluid in order todirect it into the cooling holes 20.

The nozzle 19 of eductor tube 18 is pointed into axial cooling hole 20which extends an axial distance through a portion of the turbine casing2 and a portion of the exhaust barrel 14, passing across the connectingjoint therebetween. The entrance to cooling hole 20 is generally roundedas indicated at 21 in order to facilitate the mixing and smooth flow ofthe pressurized fluid and secondary fluid. It will be appreciated thatthe portion of turbine casing or exhaust casing, having coolant holes20, will necessarily be of sufficient thickness to accommodate saidholes without causing unwanted structural weakness. The cooling holesmay be cast or machined directly into the casing walls.

As shown by FIG. 3, the eductor tube 18 is mounted in a recess or well22 on the turbine casing 2. The reason for mounting the eductor tubes inwell 22 is to minimize the easing thickness required to accommodatecooling holes 20. Tube 18 is secured in its proper position by anysuitable means, for example, by nut 24.

As is shown in the embodiment of FIG. 3, the cooling holes 20 may havesloping walls in order to form a diffuser. The advantage of having sucha construction will be further described in the operation of theinvention, but in general better cooling results from using a diffusersection.

OPERATION The operation of the present invention is as follows. Amultiplicity of eductor tubes with nozzles are uniformly spaced aroundthe turbine casing. A source of pressurized fluid, air in the principaldescription, is available which may be comprised of clean compressorextraction air. The pressurized fluid is directed to chamber 9 or ringmanifold 32 from where it flows through eductor tube 18. As thepressurized fluid passes through nozzle 19, it provides the requiredmomentum of a high velocity stream to accelerate and carry a secondaryfluid, atmospheric air in the principal description, through the coolingholes against a small pressure head. It will be appreciated that byutilizing a small amount of pressurized fluid from the cycle air in sucha manner, a great amount of total cooling air flow is realized ascompared to the design where cycle air alone is utilized. Only 10-15percent of the total cooling medium is obtained from cycle fluid, thusmaintaining a high cycle efficiency while greatly increasing coolingcharacteristics. As the cooling medium passes through the cooling holes,it removes heat from the casing material. The amount of flow through thecoolant holes, of course, determines the amount of cooling. Byincreasing the diameter of the eductor tubes, a greater amount ofprimary air would mix with secondary fluid, thereby causing a greaterflow rate which increases the cooling rate. Another method of increasingthe flow rate is to incorporate a diffuser, as previously mentioned,which will result in the additional pressure recovery needed to increasethe flow rate. The rounded corners at the entrance to cooling holes 19provide an efficient transition surface when the pressurized fluid ismixing with the secondary fluid and entering the coolant hole. After thecooling medium passes through the cooling holes, it enters chamber 15where it cools both the outer barrel l4 and diffuser sidewall 13 beforepassing through and cooling struts 12. After passing through the struts,the cooling medium is directed by appropriate means to the atmosphere,cooling other elements in its path. It should be noted that the coolingmedium may be exhausted into the atmosphere at an earlier point if suchoperation is desired.

As a direct benefit of using atmospheric air as the secondary fluid,outer compartment ventilation is realized. in the embodiment shown, theouter compartment is formed by the cooperation of a weatherproof coverand the turbine casings as previously mentioned. As the pressurizedfluid exhausts from the nozzle and into the cooling hole, it drawssecondary air with it, thus serving to ventilate the compartment.

Thus, it will be appreciated that a cooling system for a gas turbine hasbeen described which utilizes a minimum of cycle fluid and employs nomoving parts. A simple eductor cooling system operates to accomplish thecomplete cooling of the hot casing areas of the gas turbine while at thesame time providing compartment ventilation should an outer covering beutilized.

it may occur to others of ordinary skill in the art to makemodifications of this invention which will remain within the concept andscope thereof and will not constitute a departure therefrom.Accordingly, it is intended that the invention be not limited by thedetails in which it has been described but that it encompass all withinthe purview of the following claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An eductor cooled gas turbine comprising:

a gas turbine casing including a solid annular wall portion ofsubstantial thickness and axial length,

a plurality of cooling holes about the circumference of said casingextending through said casing inside said wall portion thickness alongthe length thereof and open at each end,

a source of pressurized fluid, and

a plurality of eductor tubes disposed about the circumference of saidcasing and connected to said source so as to direct said pressurizedfluid into one end of said cooling holes.

2. A gas turbine according to claim 1 in which said pressurized fluidsource comprises compressed cycle air extracted from the compressorsection of said gas turbine.

3. A gas turbine according to claim 1 in which said pressurized sourcecomprises fluid from an external source.

4. A gas turbine according to claim 1 in which said cooling holes extendthrough first and second portions of said casing disposed on either sideof a connecting joint and communicate with the atmosphere at both endsthereof.

5. A gas turbine according to claim 1 in which said eductor tubes have anozzle portion on one end so that said pressurized fluid will providethe momentum to accelerate a secondary fluid surrounding said casingthrough said cooling holes.

6. A gas turbine according to claim 1 in which said cooling holes haverounded entrances to facilitate the mixing of said secondary fluid withsaid pressurized fluid.

7. A gas turbine according to claim 1 in which said cooling holes have adiffuser section for additional pressure recovery.

8. A gas turbine according to claim 1 in which one end of said coolingholes communicates with hollow struts supporting an exhaust frame sothat said struts are cooled by the flow therethrough the cooling medium.

9. A gas turbine according to claim 8 in which said cooling medium flowsthrough said struts and thereafter exhausts to the atmosphere.

10. A gas turbine according to claim 1 which is surrounded by an outercovering for protection from inclement weather and in which said eductorcooling provides turbine compartment ventilation.

1. An eductor cooled gas turbine comprising: a gas turbine casingincluding a solid annular wall portion of substantial thickness andaxial length, a plurality of cooling holes about the circumference ofsaid casing extending through said casing inside said wall portionthickness along the length thereof and open at each end, a source ofpressurized fluid, and a plurality of eductor tubes disposed about thecircumference of said casing and connected to said source so as todirect said pressurized fluid into one end of said cooling holes.
 2. Agas turbine according to claim 1 in which said pressurized fluid sourcecomprises compressed cycle air extracted from the compressor section ofsaid gas turbine.
 3. A gas turbine according to claim 1 in which saidpressurized source comprises fluid from an external source.
 4. A gasturbine according to claim 1 in which said cooling holes extend throughfirst and second portions of said casing disposed on either side of aconnecting joint and communicate with the atmosphere at both endsthereof.
 5. A gas turbine according to claim 1 in which said eductortubes have a nozzle portion on one end so that said pressurized fluidwill provide the momentum to accelerate a secondary fluid surroundingsaid casing through said cooling holes.
 6. A gas turbine according toclaim 1 in which said cooling holes have rounded entrances to facilitatethe mixing of said secondary fluid with said pressurized fluid.
 7. A gasturbine according to claim 1 in which said cooling holes have a diffusersection for additional pressure recovery.
 8. A gas turbine according toclaim 1 in which one end of said cooling holes communicates with hollowstruts supporting an exhaust frame so that said struts are cooled by theflow therethrough of cooling medium.
 9. A gas turbine according to claim8 in which said cooling medium flows through said struts and thereafterexhausts to the atmosphere.
 10. A gas turbine according to claim 1 whichis surrounded by an outer covering for protection from inclement weatherand in which said eductor cooling provides turbine compartmentventilation.